NOAA Paleoclimatology Program. The National Oceanic and Atmospheric Administration--National Environmental Satellite, Data, and Information Service--National Climatic Data Center have created a web site that explains and helps us study what went on, climatologically, in the past. This type of information can help scientists make better predictions about what will occur in the future. "Paleoclimatologists use clues from natural 'proxy' sources such as tree rings, ice cores, corals, and ocean and lake sediments to understand natural climate variability." Before you dig too deeply into this site, you may want to have a look at the Paleoclimatology Primer, which provides an overview and perspective.
A collection of slide sets is available; topics include The Ice Ages, Climate and the Classic Maya Civilization, Coral Paleoclimatology: Natural Record of Climate change for High School Student, Polar Ice Cores, and Tree Rings: Ancient Chronicles of Environmental Change. A Climate Timeline Information Tool -- which includes Climate Science (processes) and Climate History (events) pulls it all together for you.
The site features an extensive collection of data sets, accessible via a search form that facilitates queries by investigator name, geographic location, data type and other attributes. To get an idea of how this data is used, take a look at the archive of climate reconstructions "of past temperature, precipitation, vegetation, streamflow, sea surface temperature, and other climatic or climate-dependent conditions."
The interested non-scientist might enjoy looking through Paleo Perspectives, a set of three comprehensive websites that explore abrupt climate change, North American drought, and global warming. An Education & Outreach page offers pointers to information and resources that may be useful to teachers and students. Personally, I was fascinated by Henri D. Grissino-Mayer's Ultimate Tree-Ring Web Pages; Dr. Grissino-Mayer is a professor in the Department of Geography at the University of Tennessee. It includes an extensive gallery of photos of interest to dedrochronologists.